Compute Cgk = min(USL−x̄, x̄−LSL)/(3·s), a bias-aware capability index measuring whether a system is both accurate and precise.
输入上下规格限、测量均值与标准差，求 Cgk。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Capability index including bias | Cgk = ( tolerance/2 - |bias| ) / ( (K/2) · sigma_m ), commonly with K = 6 | ISO 22514-7:2012, Statistical methods in process management - Capability of measurement processes |
| Relation to Cg | With zero bias, Cgk reduces to Cg; larger bias lowers Cgk | ISO 22514-7:2012, Statistical methods in process management - Capability of measurement processes |
| Acceptance criterion | Cgk ≥ 1.33 is the usual acceptance threshold | ISO 22514-7:2012, Statistical methods in process management - Capability of measurement processes |
| Origin of bias | Bias = mean measured value - reference value, an uncorrected systematic effect | JCGM 200:2012, International Vocabulary of Metrology (VIM) |